Book excerpt: Identity is defined in many different ways in various disciplines in the social sciences and sub-disciplines within psychology. The developmental psychological approach to identity is characterized by a focus on developing a sense of the self that is temporally continuous and unified across the different life spaces that individuals inhabit. Erikson proposed that the task of adolescence and young adulthood was to define the self by answering the question: Who Am I? There have been many advances in theory and research on identity development since Erikson's writing over fifty years ago, and the time has come to consolidate our knowledge and set an agenda for future research. The Oxford Handbook of Identity Development represents a turning point in the field of identity development research. Various, and disparate, groups of researchers are brought together to debate, extend, and apply Erikson's theory to contemporary problems and empirical issues. The result is a comprehensive and state-of-the-art examination of identity development that pushes the field in provocative new directions. Scholars of identity development, adolescent and adult development, and related fields, as well as graduate students, advanced undergraduates, and practitioners will find this to be an innovative, unique, and exciting look at identity development.